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Methodology of ApMV, ACLSV and ASGV diagnostic in apple and pear cultivars and rootstocks by ELISA
Svoboda, Jiří ; Polák, Jaroslav
The presence of Apple mosaic virus (ApMV), Apple chlorotic leaf spot virus (ACLSV) and Apple stem grooving virus (ASGV) is tested in apple and pear cultivars and rootstocks according to the EPPO recommendation by evaluating symptoms on tree indicators after grafting. This method requires two or three years of planting. For that reason it was prepared and optimised serological testing the presence of ApMV, ACLSV and ASGV by ELISA as a reliable specific methodology. Research results obtained in Crop Research Institute, Prague approve suitability of ELISA for the detection of these viruses in a specific tree tissue during a specific vegetation period. Developed methodological procedures are appropriate especially for state control and supervision laboratories and they are necessary for the certification scheme of fruit trees.
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Fatigue properties of nickel-base superalloy inconel 792-5A at 800°C
Šmíd, Miroslav ; Obrtlík, Karel ; Petrenec, Martin ; Polák, Jaroslav ; Hrbáček, K.
Smooth specimens were cyclically strained under strain control with constant strain amplitude and constant strain rate. Low cycle fatigue tests were conducted in servo-hydraulic pulsator MTS equipped with a three zone resistance furnace at temperature 800°C in air. Fracture surface was studied in SEM after fatigue test termination. Selected specimens were used to prepare foils for the transmission electron microscope (TEM) observation of microstructure and dislocation arrangement. They were used to obtain cyclic hardening/softening curves, cyclic stress-strain curve and fatigue life curves in the representation of stress amplitude, total strain amplitude and plastic strain amplitude versus number of cycles to fracture. Experimental points can be approximated with the Manson-Coffin law and the Basquin law. Fracture surface examinations revealed fatigue crack initiation sites.
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Kinetics of fatigue crack growth in Eurofer 97 steel
Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
The fatigue crack growth rate in the Eurofer 97 steel was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch. No artificial crack starters were used. The growth of semicircular cracks of length between 10 – 2000 m were measured in symmetrical tension-compression cycling with constant strain amplitude (R = -1). Long crack data were measured using standard CT specimen and ASTM methodology in stress control with R = 0.1. The growth of fatigue cracks with length in the range of 10 – 30 mm was determined. It is shown that the crack growth rate of both types of cracks are in a very good agreement if J-integral rep-resentation is used and reasonable assumptions of the crack closure effects are taken into account.
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Fatigue life and fatigue fracture of nickel-based superalloy Inconel 792-5A at room and at elevated temperatures
Šmíd, Miroslav ; Obrtlík, Karel ; Petrenec, Martin ; Polák, Jaroslav ; Hrbáček, K.
The aim of the present work is to study the effect of temperature on the fatigue life and fracture in cast polycrystalline nickel base superalloy Inconel 792-5A. Surface relief and fracture surface observations help to elucidate fatigue damage mechanism in the material used to produce the most critical component of gas turbines. Fatigue live curves can by approximated by the Manson-Coffin and Basquin law. Special attention was paid to the cyclic strain localisation on the specimen surface. Specimens strained with different strain amplitudes were used for fractographic investigation at each temperature. Both, the surface relief and the fracture surface observations, provide data on fatigue crack initiation. Detailed study of fracture surface topography was performed at all temperatures and different strain amplitudes and typical morphologies are documented. Fatigue damage mechanisms and crack path are discussed in relation to temperature, strain amplitude and crack lenght.
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Růst krátkých trhlin ve feriticko-perliticko-bainitické oceli
Polák, Jaroslav
The initiation and the growth of short cracks were studied in ferritic-pearlitic-bainitic steel. Short cracks initiate preferably in persistent slip markings in areas of proeutectoid ferrite. The kinetics of short crack growth is characterized by exponential growth. Crack growth coefficient was found to be a function of plastic strain amplitude. The comparison of the short crack growth kinetics with Coffin-Manson law allows determining the parameters of the short crack growth law from the low cycle fatigue experiments
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Fatigue properties of Eurofer steel developed for fusion application
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
In this study fatigue properties of Eurofer 97 steel in room temperatures were measured. Fatigue parameters of the cyclic stress - strain curve and fatigue life curves (Coffin-Manson curve and derived Wöhler curve) were evaluated. Major attention was given to the measurement of kinetics of fatigue crack growth by two different methods. The initiation sites of fatigue cracks and short crack growth were observed and measured on cylindrical specimens with shallow notch. These cracks had a length from 20 micrometers to 1 mm. Kinetics of growth of long cracks with the length 15-30 mm was measured on CT specimens. It was found that results obtained by the both methods are in a good agreement if the J-integral is used. It was possible to determine the threshold values of J-integral and stress intensity factor and to calculate the Paris law parameters.
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Low cycle fatigue on Inconel 713L and Inconel 792-5A superalloys at 500 A 700 °C
Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav ; Hrbáček, K. ; Kruml, Tomáš
Cylindrical specimens of cast polycrystalline nickel base superalloys Inconel 713LC and 792-5A were cyclically strained under total strain control at500°C and at700°C.Structural characteristics and morphology of gama´ precipitates of both materials are documented. Dislocations structures were studied using transmission electron microscopy using technique of oriented foils in selected specimens cyclically strained up to failure. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained for both temperatures. Cyclic hardening/softening curves depend both on temperature and plastic strain amplitude. The cyclic stress-strain curves can be approximated by power law. Experimental points of fatigue life curves satisfy the Manson-Coffin and Basquin law. Stress-strain response and fatigue life characteristics are compared at both temperatures and discussed in relative to structural parameters and to dislocation structures of superalloys studied.
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Růst krátkých trhlin z vrubů ve dvoufázové austenitcko-feritické oceli
Kotecký, Ondřej ; Degallaix, S. ; Polák, Jaroslav
The effect of microstructure and stress gradient in a two-phase austenitic-ferritic steel in specimens with confined plasticity is studied. Direct optical observations and potential drop technique calibrated via the finite element method are used to measure the surface crack size and its depth and to determine the surface crack growth. The effect of stress and strain gradients on the crack propagation kinetics and crack shape is evaluated and dicussed.
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